1. Field of the Invention
This invention relates to a battery status monitoring apparatus, a saturation polarization detecting method and a dischargeable capacity detecting method, and more particularly to a battery status monitoring apparatus for monitoring the state of a battery, a saturation polarization detecting method for detecting a saturation polarization indicative of a saturated value of a drop of the terminal voltage due to the polarization which occurs when the battery is discharged, and a dischargeable capacity detecting method for detecting a dischargeable capacity of the battery.
2. Description of the Related Art
Generally, when a current is discharged from a battery, a drop in the terminal voltage of the battery occurs. This voltage drop is attributable to an internal resistance of the battery. This voltage drop increases with deterioration of the battery. The increased voltage drop changes the dischargeable capacity of the battery. Therefore, to detect the voltage drop due to the internal resistance of the battery is very important in order to know the battery status.
For this purpose, conventionally, in a battery status monitoring apparatus mounted on the vehicle, the internal resistance was detected while a starter motor was driving, thereby knowing the battery status. Otherwise, the internal resistance was acquired at any optional time to know the battery status.
Meanwhile, the voltage drop due to the above internal resistance is classified into an IR loss (pure resistance, i.e. voltage drop due to an ohmic resistance) attributable to a battery structure and a voltage drop due to a polarized resistance component (activated polarization or concentration polarization) which is attributable to a chemical reaction.
The IR loss described above does not vary as long as the battery status does not change. On the other hand, the voltage drop due to the polarization increases in proportion to a discharged current or discharging time, but does not exceed a saturated value. Therefore, by monitoring the point where the voltage drop due to polarization is saturated, the point where the voltage drop due to the internal resistance becomes maximum can be monitored.
However, conventionally, the internal resistance was detected at the start, or any optional internal resistance was detected. The point when the polarization is saturated was not consciously monitored. Particularly, because the time while the discharged current flows at the start is very short, the internal resistance at the point when the polarization is not saturated was detected. Therefore, there is a problem that the battery status was not known correctly.